Some embodiments of DC to DC converters charge an inductor for a period. The inductor is then discharged into a capacitor. Discharging the inductor into the capacitor changes the voltage across the capacitor. The capacitor voltage is the output voltage, although in some embodiments, the capacitor voltage is filtered to remove noise and the filtered voltage is the output voltage. The charging and discharging of the inductor is similar to a pulse width modulation system whereby the lengths of the charging and/or discharging determines the output voltage.
Some of the DC-DC converters use current mode control, which controls the output voltage based on the current passing through the inductor. Current mode control is susceptible to sub-harmonic oscillation for duty cycles greater than fifty percent in peak mode and duty cycles less than fifty percent in valley mode. Peak mode is where the current peaks are controlled and valley mode is where current valleys are controlled. The sub-harmonic oscillations cause noise and inaccurate DC to DC conversions.